feat(weather): parse an Open-Meteo cache instead of OWM JSON

WMO codes to glyphs and words, moon phase, UV and AQI roles, and a
parser for the tab-separated cache the fetcher will write. Groundwork
for the Mirage-derived forecast cards.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

1 files changed, 165 insertions, 144 deletions

diff --git a/lib/weather.lua b/lib/weather.lua
index 8ecd273..aea630e 100644
--- a/lib/weather.lua
+++ b/lib/weather.lua
@@ -1,98 +1,146 @@
--- OpenWeatherMap domain knowledge and cache parsing.
+-- Open-Meteo domain knowledge and cache parsing.
 --
--- Separate from lib/data.lua: that reads /proc and /sys, this reads a cached
--- HTTP response and carries its own tables. Same testable shape though, every
--- function takes a string or numbers and returns a value, so the tests need no
--- filesystem and no network.
+-- Separate from lib/data.lua: that reads /proc and /sys, this reads the cache
+-- bin/weather-fetch.sh flattens Open-Meteo's responses into. Same testable
+-- shape though, every function takes a string or numbers and returns a value,
+-- so the tests need no filesystem and no network.
+--
+-- The forecast cards built on this (hourly, week, details, sky) are adapted
+-- from the Conky-Mirage theme by alexsson-xexpanderx:
+-- https://github.com/alexsson-xexpanderx/Conky-themes/tree/master/Conky-Mirage
 --
 -- Nothing here raises. A Lua error in this project is a blank screen, so every
 -- parse path returns nil and lets the widget draw its "no data" state.
 
 local M = {}
 
+M.CACHE = (os.getenv('XDG_CACHE_HOME') or ((os.getenv('HOME') or '') .. '/.cache'))
+  .. '/udt/weather.txt'
+
 -- Nerd Font codepoints, all present in Inconsolata Nerd Font (card.FONT_MONO).
 -- Verified by rendering the glyphs and looking at them, not by fontconfig
 -- alone: a missing glyph draws as an invisible blank rather than an error.
 M.ICON = {
-  thunder_day       = '\u{E30F}',
-  thunder_night     = '\u{E32A}',
-  drizzle_day       = '\u{E306}',
-  drizzle_night     = '\u{E326}',
-  drizzle_heavy_day = '\u{E308}',
-  drizzle_heavy_night = '\u{E325}',
-  rain_day          = '\u{E308}',
-  rain_night        = '\u{E325}',
-  snow              = '\u{E31A}',
-  fog               = '\u{E313}',
-  tornado           = '\u{E351}',
-  clear_day         = '\u{E30D}',
-  clear_night       = '\u{E32B}',
-  few_day           = '\u{E302}',
-  few_night         = '\u{E379}',
-  overcast          = '\u{E312}',
-  unknown           = '\u{E374}',
-  sunrise           = '\u{E34C}',
-  sunset            = '\u{E34D}',
+  thunder_day   = '\u{E30F}',
+  thunder_night = '\u{E32A}',
+  drizzle_day   = '\u{E306}',
+  drizzle_night = '\u{E326}',
+  rain_day      = '\u{E308}',
+  rain_night    = '\u{E325}',
+  snow          = '\u{E31A}',
+  fog           = '\u{E313}',
+  clear_day     = '\u{E30D}',
+  clear_night   = '\u{E32B}',
+  few_day       = '\u{E302}',
+  few_night     = '\u{E379}',
+  overcast      = '\u{E312}',
+  unknown       = '\u{E374}',
 }
 
--- Condition id to icon, by upper bound. Ported from the polybar script's
--- accumulated knowledge; the ranges are not round hundreds.
--- `now`, `sunrise` and `sunset` are unix timestamps and pick the day or night
--- face for the conditions that have both.
-function M.icon(id, now, sunrise, sunset)
-  if type(id) ~= 'number' then return M.ICON.unknown end
-  -- `now` is guarded alongside sunrise and sunset, not just them: comparing a
-  -- nil now against a number raises, and a raise here is a blank dashboard.
-  -- Missing any of the three means the sun is unknown, so the day face is
-  -- drawn, which is what is_day() falls back to as well.
-  local day = true
-  if now and sunrise and sunset then day = (now >= sunrise and now <= sunset) end
-  local function pick(d, n) return day and d or n end
-
-  if id <= 232 then return pick(M.ICON.thunder_day, M.ICON.thunder_night)
-  elseif id <= 311 then return pick(M.ICON.drizzle_day, M.ICON.drizzle_night)
-  elseif id <= 321 then return pick(M.ICON.drizzle_heavy_day, M.ICON.drizzle_heavy_night)
-  elseif id <= 531 then return pick(M.ICON.rain_day, M.ICON.rain_night)
-  elseif id <= 622 then return M.ICON.snow
-  elseif id <= 771 then return M.ICON.fog
-  elseif id == 781 then return M.ICON.tornado
-  elseif id == 800 then return pick(M.ICON.clear_day, M.ICON.clear_night)
-  elseif id == 801 then return pick(M.ICON.few_day, M.ICON.few_night)
-  elseif id <= 804 then return M.ICON.overcast
+-- WMO weather code to glyph. The codes are sparse groups, not ranges, so a
+-- code in a gap is unknown rather than borrowed from a neighbour.
+-- `is_day` false picks the night face; nil (unknown) draws the day face, which
+-- is what is_day() falls back to as well.
+function M.icon(code, is_day)
+  if type(code) ~= 'number' then return M.ICON.unknown end
+  local d = is_day ~= false
+  local I = M.ICON
+  if code == 0 then return d and I.clear_day or I.clear_night
+  elseif code == 1 or code == 2 then return d and I.few_day or I.few_night
+  elseif code == 3 then return I.overcast
+  elseif code == 45 or code == 48 then return I.fog
+  elseif code >= 51 and code <= 57 then return d and I.drizzle_day or I.drizzle_night
+  elseif (code >= 61 and code <= 67) or (code >= 80 and code <= 82) then
+    return d and I.rain_day or I.rain_night
+  elseif (code >= 71 and code <= 77) or code == 85 or code == 86 then return I.snow
+  elseif code >= 95 and code <= 99 then return d and I.thunder_day or I.thunder_night
   end
-  return M.ICON.unknown
+  return I.unknown
 end
 
--- OWM's metric units report wind in m/s. The card shows km/h.
-function M.kmh(ms)
-  if type(ms) ~= 'number' then return nil end
-  return ms * 3.6
+local DESCRIBE = {
+  [0] = 'Clear sky', [1] = 'Mainly clear', [2] = 'Partly cloudy', [3] = 'Overcast',
+  [45] = 'Fog', [48] = 'Rime fog',
+  [51] = 'Light drizzle', [53] = 'Drizzle', [55] = 'Dense drizzle',
+  [56] = 'Freezing drizzle', [57] = 'Freezing drizzle',
+  [61] = 'Light rain', [63] = 'Rain', [65] = 'Heavy rain',
+  [66] = 'Freezing rain', [67] = 'Freezing rain',
+  [71] = 'Light snow', [73] = 'Snow', [75] = 'Heavy snow', [77] = 'Snow grains',
+  [80] = 'Rain showers', [81] = 'Rain showers', [82] = 'Violent showers',
+  [85] = 'Snow showers', [86] = 'Snow showers',
+  [95] = 'Thunderstorm', [96] = 'Thunderstorm, hail', [99] = 'Thunderstorm, hail',
+}
+
+-- WMO code in words. Reading a nil key from a table is not an error.
+function M.describe(code)
+  return DESCRIBE[code] or 'Unknown'
 end
 
--- Beaufort force from km/h. Upper bounds carried over from the polybar
--- script; a value equal to a bound stays in the lower force.
---
--- The scale starts at 0 and ipairs starts at 1, so force N's upper bound is
--- BEAUFORT[N + 1] and the loop index is already N + 1. Hence `force - 1`
--- below. The scale tops out at 12, which is why the fall-through returns it.
-local BEAUFORT = { 1, 5, 11, 19, 28, 38, 49, 61, 74, 88, 102, 117 }
-
-function M.beaufort(kmh)
-  if type(kmh) ~= 'number' then return nil end
-  for force, bound in ipairs(BEAUFORT) do
-    if kmh <= bound then return force - 1 end
-  end
-  return 12
+local function round(v) return math.floor(v + 0.5) end
+
+-- A temperature as the cards print it. Missing is '--', never '0': zero is a
+-- legitimate reading. The '-0' a value just under zero would round to is
+-- folded into '0'.
+function M.deg(v)
+  if type(v) ~= 'number' then return '--' end
+  local r = round(v)
+  if r == 0 then r = 0 end
+  return string.format('%d\u{00B0}', r)
+end
+
+-- A rounded number with an optional suffix, or '--'.
+function M.num(v, suffix)
+  if type(v) ~= 'number' then return '--' end
+  return string.format('%d', round(v)) .. (suffix or '')
+end
+
+-- The fetcher asks Open-Meteo for km/h or mph to match UNITS.
+function M.wind_unit(units)
+  return units == 'imperial' and 'mph' or 'km/h'
+end
+
+-- Seconds as '10h 28m'.
+function M.duration(s)
+  if type(s) ~= 'number' or s < 0 then return '--' end
+  return string.format('%dh %02dm', math.floor(s / 3600), math.floor(s % 3600 / 60))
+end
+
+-- Threshold role names, which index the palette (colors.ok and so on).
+-- UV: WHO bands, low under 3, very high from 8.
+function M.uv_role(uv)
+  if type(uv) ~= 'number' then return nil end
+  if uv >= 8 then return 'critical' elseif uv >= 3 then return 'warning' end
+  return 'ok'
+end
+
+-- European AQI: good and fair up to 40, moderate and poor up to 80.
+function M.aqi_role(aqi)
+  if type(aqi) ~= 'number' then return nil end
+  if aqi > 80 then return 'critical' elseif aqi > 40 then return 'warning' end
+  return 'ok'
+end
+
+-- Moon phase from the mean synodic month against a known new moon
+-- (2000-01-06 18:14 UTC). Returns phase 0..1 (0 new, 0.5 full) and the lit
+-- fraction 0..1. The mean month is off the true one by under a day, which a
+-- 28-step glyph cannot show anyway.
+local SYNODIC = 29.530588853
+local NEW_MOON = 947182440
+
+function M.moon(epoch)
+  if type(epoch) ~= 'number' then return nil end
+  local phase = ((epoch - NEW_MOON) / 86400 / SYNODIC) % 1
+  return phase, (1 - math.cos(2 * math.pi * phase)) / 2
+end
+
+-- One of the 28 Nerd Font moon glyphs, U+E38D (new) to U+E3A8, in phase order.
+function M.moon_icon(phase)
+  if type(phase) ~= 'number' then return M.ICON.unknown end
+  return utf8.char(0xE38D + round(phase * 28) % 28)
 end
 
 -- Eight compass points. The half-step offset is what makes north straddle
--- zero: without it, 350 degrees would land in NW and 10 in NE, leaving north
--- with only half its arc.
---
--- Nothing calls compass() yet: the card draws arrow() instead. It is kept
--- because it shares arrow()'s binning exactly, so testing both pins that
--- shared logic from two angles, and swapping the card to read "S 9 km/h"
--- instead of an arrow is then a one-word change rather than new code.
+-- zero: without it, 350 degrees would land in NW and 10 in NE.
 local POINTS = { 'N', 'NE', 'E', 'SE', 'S', 'SW', 'W', 'NW' }
 
 function M.compass(deg)
@@ -101,109 +149,82 @@ function M.compass(deg)
   return POINTS[i + 1]
 end
 
--- Arrow glyphs, in the same order as POINTS but rotated half a turn: OWM
--- reports the direction the wind comes FROM, and an arrow reads as the
--- direction it goes TO.
-local ARROWS = { '\u{2193}', '\u{2199}', '\u{2190}', '\u{2196}',
-                 '\u{2191}', '\u{2197}', '\u{2192}', '\u{2198}' }
-
-function M.arrow(deg)
-  if type(deg) ~= 'number' then return '' end
-  local i = math.floor(((deg % 360) + 22.5) / 45) % 8
-  return ARROWS[i + 1]
-end
-
 -- Fraction of daylight elapsed, clamped to 0..1.
 --
--- OWM returns TODAY's sunrise and sunset, so before dawn this is negative and
--- after dusk it is over 1. Clamping parks the dot at the corresponding end of
--- the arc, which is the cheap correct-enough behaviour; multi-day astronomy
--- buys nothing for a dot on a curve.
+-- The cache carries TODAY's sunrise and sunset, so before dawn this is
+-- negative and after dusk it is over 1. Clamping parks the dot at the
+-- corresponding end of the arc.
 function M.sun_t(now, sunrise, sunset)
   if type(now) ~= 'number' or type(sunrise) ~= 'number'
      or type(sunset) ~= 'number' then return nil end
   local span = sunset - sunrise
   if span <= 0 then return 0 end   -- polar day/night or bad data: no division
-  -- ponytail: a NaN timestamp slips through, since NaN is a number and every
-  -- comparison against it is false, so both clamps below fall through and this
-  -- returns NaN. Unreachable today: parse() matches %d+ for the sun times and
-  -- `now` is os.time(). Cairo ignores a NaN coordinate, so the cost would be a
-  -- missing dot, not a crash. Guard it here if a caller ever computes `now`.
   local t = (now - sunrise) / span
   if t < 0 then return 0 elseif t > 1 then return 1 end
   return t
 end
 
--- Whether the sun is up. Inclusive at both ends, matching the polybar script's
--- comparison, so the instant of sunrise draws the day face.
+-- Whether the sun is up. Inclusive at both ends; unknown falls back to day.
 function M.is_day(now, sunrise, sunset)
   if type(now) ~= 'number' or type(sunrise) ~= 'number'
      or type(sunset) ~= 'number' then return true end
   return now >= sunrise and now <= sunset
 end
 
--- Parse the cached OWM response.
+-- Parse the cache: tab-separated records, first field the record type.
 --
--- Lua patterns, not a JSON library: the current-weather response is flat and
--- its shape is known, so six scalars do not justify a dependency. Returns nil
--- on anything unreadable, never an error.
+--   units   metric
+--   current epoch temp feels code is_day humidity wind wind_deg
+--   sun     sunrise sunset
+--   air     european_aqi
+--   hour    epoch temp code precip_prob is_day uv      (24 of them)
+--   day     epoch code min max precip_prob             (7 of them)
+--
+-- A field Open-Meteo left null arrives as the word 'null', which tonumber
+-- turns into nil. Returns nil when current, sun or every hour is missing:
+-- a partial card is worse than an honest "no data".
 function M.parse(src)
   if type(src) ~= 'string' or src == '' then return nil end
-
-  -- Scalars are matched inside their own object where the key would otherwise
-  -- be ambiguous. "temp" appears as a prefix of "temp_min" and "temp_max", so
-  -- it is anchored to the character that follows it.
-  local function num(pat)
-    return tonumber(src:match(pat))
+  local w = { hours = {}, days = {} }
+  for line in src:gmatch('[^\n]+') do
+    local f = {}
+    for field in (line .. '\t'):gmatch('([^\t]*)\t') do f[#f + 1] = field end
+    local function n(i) return tonumber(f[i]) end
+    local kind = f[1]
+    if kind == 'units' then
+      w.units = f[2]
+    elseif kind == 'current' then
+      w.current = { dt = n(2), temp = n(3), feels = n(4), code = n(5),
+                    is_day = n(6) ~= 0, humidity = n(7), wind = n(8),
+                    wind_deg = n(9) }
+    elseif kind == 'sun' then
+      w.sun = { rise = n(2), set = n(3) }
+    elseif kind == 'air' then
+      w.air = { aqi = n(2) }
+    elseif kind == 'hour' then
+      w.hours[#w.hours + 1] = { t = n(2), temp = n(3), code = n(4),
+                                precip = n(5), is_day = n(6) ~= 0, uv = n(7) }
+    elseif kind == 'day' then
+      w.days[#w.days + 1] = { t = n(2), code = n(3), min = n(4), max = n(5),
+                              precip = n(6) }
+    end
+  end
+  if not (w.current and w.current.temp and w.sun and w.sun.rise and w.sun.set
+          and #w.hours > 0) then
+    return nil
   end
-
-  local main = src:match('"main"%s*:%s*(%b{})') or ''
-  local wind = src:match('"wind"%s*:%s*(%b{})') or ''
-  local sys  = src:match('"sys"%s*:%s*(%b{})') or ''
-  local cond = src:match('"weather"%s*:%s*%[%s*(%b{})') or ''
-
-  local w = {
-    id          = tonumber(cond:match('"id"%s*:%s*(%-?%d+)')),
-    description = cond:match('"description"%s*:%s*"([^"]*)"'),
-    -- The exponent is accepted although OWM has never been seen to emit one:
-    -- a pattern stopping at the 'e' would read 1.8e1 as 1.8 and draw 2 degrees
-    -- instead of 18, silently and plausibly. Cheaper to accept than to detect.
-    temp        = tonumber(main:match('"temp"%s*:%s*(%-?[%d%.eE%+%-]+)')),
-    feels_like  = tonumber(main:match('"feels_like"%s*:%s*(%-?[%d%.eE%+%-]+)')),
-    humidity    = tonumber(main:match('"humidity"%s*:%s*(%d+)')),
-    wind_speed  = tonumber(wind:match('"speed"%s*:%s*([%d%.eE%+%-]+)')),
-    wind_deg    = tonumber(wind:match('"deg"%s*:%s*(%d+)')),
-    sunrise     = tonumber(sys:match('"sunrise"%s*:%s*(%d+)')),
-    sunset      = tonumber(sys:match('"sunset"%s*:%s*(%d+)')),
-    city        = src:match('"name"%s*:%s*"([^"]*)"'),
-    dt          = num('"dt"%s*:%s*(%d+)'),
-  }
-
-  -- Without these the card has nothing to draw, and a partial card is worse
-  -- than an honest "no data". An API error body fails here too: it carries a
-  -- cod and a message, no weather.
-  if not (w.id and w.temp and w.sunrise and w.sunset) then return nil end
   return w
 end
 
 -- Three missed fetches at the 15-minute interval.
 M.STALE_AFTER = 45 * 60
 
--- `now` is guarded alongside `dt` although every caller passes os.time(),
--- which cannot be nil: these were the only two functions in the module that
--- did arithmetic on an unchecked argument, and the module's promise is that
--- nothing raises. A raise here is a blank dashboard.
 function M.is_stale(dt, now)
   if type(dt) ~= 'number' or type(now) ~= 'number' then return true end
   return (now - dt) > M.STALE_AFTER
 end
 
--- Short age for the marker beside the city: "12m", "3h", "2d".
---
--- A negative age is clamped to zero rather than printed. An observation
--- timestamped in the future means a clock skew somewhere, and "stale -17m" on
--- the card reads as a broken widget; treating it as fresh is both tidier and
--- truer, since weather from the future is not old.
+-- Short age: "12m", "3h", "2d". A negative age (clock skew) reads as fresh.
 function M.age_str(dt, now)
   if type(dt) ~= 'number' or type(now) ~= 'number' then return '?' end
   local s = now - dt